Hot gas engine with co-axial cylinder bores of differing diameter

ABSTRACT

A Stirling engine has two cylinders one having a higher and one having a lower pressure working space interconnected by a regenerator cooler array. The two cylinders and accompanying pistons are disposed at 90* with each cylinder having co-axial bores and associated pistons of different diameters separated by shoulder surfaces having sharp edges. A crankcase is disposed adjacent the larger diameter bores of both cylinders. A space between the two cylinders is connected to the crankcase by a conduit including a non-return valve, and the crankcase is connected to the lower pressure working space by a conduit with a restricted area orifice or a non-return valve.

United States Patent [191 Greis 1 May28, 1974 HOT GAS ENGINE WITH CO-AXIAL CYLINDER BORES OF DIFFERING Sweden Filed: Dec. 15, 1972 Appl. No.1 315,479

[ 30] I Foreign A'pbfifiidii Ii iority fiata Dec. 21, 1971 Great Britain ..59267/71 U.S. CL". .L... 6075 7, 927153 Int. Cl. F02g l/04 Field of Search 123/74, 71 195 R; 92/86 References Cited UNITED STATES PATENTS Wilson 60/24 X Brown 123/195 RX Primary ExaminerE dgar W. Geoghegan Assistant ExaminerAllen M. Ostrager Attorney, Agent, or Firm-Laurence R. Brown, Esq.

[5 7 1 ABSTRACT A Stirling engine has two cylinders one having a higher and one having a lower pressure working space interconnected by a regenerator cooler array. The two cylinders and accompanying pistons are disposed at 90 with each cylinder having co-axial bores and associated pistons of different diameters separated by shoulder surfaces having sharp edges. A crankcase is disposed adjacent the larger diameter bores of both cylinderssA space between the two cylinders is connected to the crankcase by a conduit including a nonreturn valve, and the crankcase is connected to the lower pressure working space by a conduit with a restricted area orifice or a non-return valve.

6 Claims, 1 Drawing Figure HOT GAS ENGINE WITH CO-AXIAL CYLINDER BORES OF DIFFERING DIAMETER This invention relates to a hot gas engine of the kind (herein called the kind defined) comprising two cylinders and two pistons each working in a respective cylinder and dividing said cylinder into an upper space and a lower space, the two upper spaces being interconnected through heater pipes, a regenerator and a cooler connected in series, and the two lower spaces communicating with a pressurised crank casing.

Hot gas engines of the kind defined may be very simple with few moving parts, and will thus be cheap in manufacture and reliable in operation. However, it is a problem that oil contained in the crank casing may pass between the pistons andthe cylinder walls tovthe upper spaces of thecylinders and cause pollution of the working gas.

The object of the present invention is to avoid or substantially reduce the risk of oil polluting the workinggas in an engine of the kind defined.

According to the invention a hot gas engine of the kind defined is characterised in that each of 'said pistons and cylinders comprises an upper part and a lower part, the upper parts being of smaller diameter than the lower parts, a shoulder surface being provided between the said two parts of each cylinder.

The scope of the monopoly sought is defined in the Claims hereinaftenand how the invention may be put into practice is described in more detail with reference to the accompanying drawing, showing schematically in vertical section a hot gas engine according to the invention.

The illustrated engine is of the kind defined and comprises a crank-casing l carrying two cylinders disposed with their axes perpendicular to each other. Each of the cylinders consists of two interconnected co-axial parts, the two upper parts 2 and 4 having smaller interior diameters than the two lower parts 3 and 5. Each cylinder contains a piston having two parts of different diameters to fit the two sections of the cylinders respectively, the smaller diameter piston parts being designated by 6 and 7 and the larger parts by 8 and 9. There are two upper spaces in the form of working chambers 10 and 11 one in each of the two cylinders above the respective piston parts 6 and 7. The working chamber 10 is maintained at a high temperature level e.g.. 700C whereas'the working chamber 11 ismaintained at a temperature which is substantially lower e.g. 80C. The

two working chambers are filled with a working gas such as hydrogen or helium and they are interconnected through a plurality of heater pipes 12 (only one of which is shown) a regenerator l3 and a cooler 14. The pistons 6, 8 and 7, 9 are connected to a crank-shaft 15 by means of connecting rods 16 and 17 respectively. The reciprocating movement of the piston 6, 8 is 90 of crank-shaft rotation in advance of the .piston 7, 9 if the crank-shaft 15 is rotating in the forward direction i.e. counter-clockwise as viewed in the drawing.

Between the walls of the cylinder parts and the piston parts are formed two lower spaces 18. Due to the difference in interior diameter of the cylinder parts the volumes of said spaces 18 will vary during each cycle of the engine. Each space 18 communicates directly with the interior of a pressurised crank-casing 1 through a conduit 19 containing a non-return valve 20 allowing flow of gas only in the direction from the respective space 18 to the interiorof the crank casing 1. Another conduit 21 containing an oil filter 22and a restricted orifice 23 connects theinterior of the crank casing l with the working chamber 11.

The operation is as follows:

During operation the two working chambers 10 and 11 will contain working gas at a high mean pressure e.g. bars. However, due to the movements of the pistons this pressure will vary during a revolution of the crank-shaft l5 say between 125 and bars. As the piston 6, 8 in the high temperature cylinder is 90 of crank-shaft rotation in advance of the piston 7, 9 in the lower temperature cylinder 4, 5 mechanical energy will be produced during each cycle.

It is of importance to prevent any of the oil necessary for lubrication of the connecting rods and the crankshaft as well as for the piston parts 8 and 9 from passing further towards the workingchambers l0 and 11. Any oil passing into said chambers will pollute the working gas and rapidly destroy the regenerator 13.

In the design shown the difference between the inner diameters of the cylinder parts 2 and 3 as well as the difference between the inner diameters of the cylinder parts 4 and 5 is used to form interior shoulder surfaces 24 and 25 having circular sharp edges 26 and 27. The said edges 26 and 27 will prevent flow of oil towards the cylinder ends remote from the crank casing.

The space 18 at each piston will be on variable volume during thepiston movements. This volume variation is used to obtain a pumping effect by connecting the space 18 with the interior of the crank casing through a path containing a respective non-return valve 20. Any leaking gas which may be mixed with oil is then continuously pumped away from the space 18 into the interior of the crank casing.

In modifications this effect could be obtained by providing non-return valves in the parts 8 and 9 of the pistons or by a suitable formation of the piston rings as is well known in the art.

The pressure in the crank casing corresponds to the mean pressure of the working cycle, due to gas flow through the conduit 21. The restricted orifice 23 could be replaced by a non-return valve allowing flow of gas only in the direction into the chamber 11. ln such a case the pressure in the crank casing would correspond to the minimum cycle pressure and the pumping effect from the'chambers 18 would 'be'improved. Also the walls of the crank casing could be made thinner and has two co-axial parts of different diameter providing a shoulder surface therebetween, and'a piston assembly with two different diameter pistons operating in each cylinder in the-respective associated parts.

4. An engine as defined in claim 1, including a conduit connected between said crankcase and one working space including means offering resistance against gas flow.

S. An engine as defined in claim 4', wherein the means offering resistance comprises a restricted portion of the conduit. 6. An engine as defined in claim duit includes oil filtering means 4, wherein said. con- 

1. A Stirling hot gas engine comprising in combination two cylinders having pistons therein and respective high and low pressure working spaces connected by a regenerator-cooling assembly, wherein each cylinder has two co-axial parts of different diameter providing a shoulder surface therebetween, and a piston assembly with two different diameter pistons operating in each cylinder in the respective associated parts.
 2. An engine as defined in claim 1, wherein a crankcase connects the two larger diameter parts of saId two cylinders.
 3. An engine as defined in claim 2, wherein a space is provided in the cylinder between the two pistons of each piston assembly, and including a conduit with a non-return valve connected between the said spaces of each cylinder and the crankcase in a direction to permit gas flow only in the direction toward the crankcase.
 4. An engine as defined in claim 1, including a conduit connected between said crankcase and one working space including means offering resistance against gas flow.
 5. An engine as defined in claim 4, wherein the means offering resistance comprises a restricted portion of the conduit.
 6. An engine as defined in claim 4, wherein said conduit includes oil filtering means. 